The present invention generally relates to machine tools, and more particularly relates to laser equipped CNC machine tools having long laser beam paths and that are used to cut and weld parts from carbon steels, stainless steel and aluminum.
Flying optic CNC laser cutting machines and cantilevered CNC laser cutting and welding machines with working areas of two meters by 4 meters and above have long beam paths, the distance between the laser and the focal optic, exceeding 8 meters in length. Individual sections of the beam path can exceed 6 meters in length. Such machines, usually having a large structural frame or base manufactured of steel, are susceptible to degradation in alignment of the beam path caused by temperature gradients in the factory in which they are used.
Cycling of shop heating and cooling equipment, opening and closing doors and windows cause temperature variations within the shop. Residual heat from operations of laser-equipped machine tools can also be a cause of temperature related effects on machine tool structures. Because cold air tends to fall and warm air tends to rise, the temperature at floor level tends to be cooler than that at elevations above the floor. Carbon Steel has a property that it expands at 0.00000633 inch per inch of length per degree Fahrenheit. Non-uniform temperatures from floor level to upper surfaces of the base cause the base to expand non-uniformly. Way mounting surfaces machined flat and straight in a uniform temperature environment crown slightly convexly in such conditions. As a result one or more machine motions may travel along an arched surface while the laser beam within the beam path travels in a straight line. Thus the position of the bending mirror(s) carried on moving machine elements may shift relative to the centerline of the laser beam as the as the bridge and cutting head travel from respective end of travel to opposite end of travel. The bending mirror(s) shifting cause the laser beam to impinge on and be reflected from a different position on the mirror than intended, thus causing the focused beam to shift from its centered position within a cutting nozzle or a welding head, and thus causing degradation of cutting or welding quality or of part accuracy.
Such machines also may have an optical carriage configured to maintain a constant length beam path, as opposed to a variable length beam path between the laser and the cutting nozzle or welding head. Such optical carriages tend to have a short wheelbase, the distance between linear bearings on a common linear way. Small deviations in flatness of the machine mounting elements and linear ways cause angular deviation in pointing of the laser beam. Small deviations are magnified by the long path length and can also be a source of alignment degradation.
It is an objective of the invention to provide a laser beam position control apparatus for a large laser equipped CNC machine tool that will automatically maintain the precise alignment of the beam path, though the machine may be operating in a non-uniform temperature environment and/or with residual heat from machine operation that may cause the machine base to crown or otherwise deviate from the intended form.
Another objective of the invention is to provide a laser beam position control apparatus, for a large laser equipped CNC machine having long beam path segments and an optical carriage with a short wheelbase, that will automatically correct for small deviations in flatness of machine mounting elements and/or linear ways that cause angular deviation in the pointing of the laser beam.
It is a preferred form and objective of the invention to monitor the position of the laser beam within the beam path as the machine is in motion, to sense when the beam is moving from its intended position, to generate an error signal indicative of position error and direction, to use the error signal as an input to a drive apparatus, and for the drive apparatus to output a corrective signal to activate a correction apparatus such that the laser beam is returned to its intended position.
It is a preferred form of the invention for the correction apparatus to consist of two actuators moving a common object to steer a laser beam.
It is an alternate form of the invention for the correction apparatus to consist of two actuators, each moving a separate object to steer the laser beam.
It is a preferred form and objective of the invention to provide a control system for the laser beam position control apparatus that, when activated, functions separately from the CNC of the laser equipped CNC machine tool.
Another objective and preferred form of the invention is to provide a laser beam position control apparatus that is adaptable to one or more axes to automatically maintain the alignment of the beam path.
Yet another objective is to provide an alternative control scheme for the laser beam position control apparatus wherein the central processor of the CNC of the laser equipped CNC machine tool performs the signal processor functions.
According to the invention, in alternative control schemes for the laser beam position control apparatus, the signal processor resides in the laser beam position sensor enclosure or in a Personal Computer (PC).